Process for manufacture of nonwoven fabrics or paper by wet sieving of viscose fibers

ABSTRACT

STAPLE FIBERS FORMED FROM STABLE INCOMPLETELY REGENERATED CELLULOSE FILAMENTS ARE DISPERSED IN WATER AND THEREAFTER FORMED INTO PAPER OR A NONWOVEN FABRIC. THE FILAMENTS, WHICH HAVE A PRIMARY SWELLING VALUE OF FROM 1900 TO 10,000, ARE FORMEDBY THE VISCOSE PROCESS WHEREIN VISCOSE IS SPUN THROUGH A SPINNERET INTO A COAGULATING BATH OF 8-18 G./1. SULFURIC ACID, 0.2-1.0 G./1. ZINC SULFATE AND 20-100 G./1. SODIUM SULFATE AT A TEMPERATURE OF FROM 15/35*C.

United States Patent O 3,553,078 PROCESS FOR MANUFACTURE OF NONWOVEN FABRICS OR PAPER BY WET SIEVING OF VIS- COSE FIBERS Yoshikazu Aoki, Otsu, and Teruji Kamei, Akira Hayami,

and Masahiro Kitano, Kyoto, Japan, assignors to Tachikawa Research Institute Higashiyama-ku, Kyoto, Japan, a corporation of Japan No Drawing. Filed Apr. 5, 1968, Ser. No. 719,247 Claims priority, application Japan, Apr. 26, 1967, 2/26,267 Int. Cl. D21f 11/00 U.S. Cl. 162157 3 Claims ABSTRACT OF THE DISCLOSURE Staple fibers formed from stable incompletely regenerated cellulose filaments are dispersed in water and thereafter formed into paper or a nonwoven fabric. The filaments, which have a primary swelling value of from 1900 to 10,000, are formed by the viscose process wherein viscose is spun through a spinneret into a coagulating bath of 8-18 g./l, sulfuric acid, 0.2-1.0 g./l. zinc sulfate and 20-100 g./l. sodium sulfate at a temperature of from 35 C.

This invention relates to a process for manufacturing rayon paper or nonwoven fabric by a wet system.

Our US. Pat. No. 3,320,117 describes and claims a process for the manufacture of rayon paper or nonwoven fabric from incompletely regenerated viscose filaments. In this process, the upper limit of the applicable primary swelling value is 2,400. This is because as stated in the description thereof, when the primary swelling value is over 2,400%, the dispersed filaments are apt to swell infinitely in water, it is impossible to make smoothly the wet sheet paper, and there is slow drainage through the wire net.

Such an upper limitation will be explained as follows. In order to obtain fibres having a high primary swelling value, the acid concentration in the spinning bath must be low, but, as the result, the inner structure of fibres does not progress to such a degree as to make the fibres fit for smooth papermaking.

We, however, have found that incompletely regenerated fibre having a high primary swelling value, i.e., from 1,900 to 10,000, can be obtained not only with facility but also in a stable state by using a relatively higher effective acid concentration bath. Of this fibre a paper sheet can be formed without any difificulty. Furthermore, we have found that the higher the primary swelling value of the fibre is, the more a paper sheet made from it resembles a textile fabric. According to the present invention there is provided a process for manufacturing rayon paper or nonwoven fabric by a wet system, which comprises dispersing in water staple fibres formed from stable incompletely regenerated cellulose filaments obtained by the viscose process, said filaments having a primary swelling value of from 1,900 to 10,000 and being obtained by spinning viscose through a spinneret having an effective length to diameter ratio for the holes such that the Barus effect on the viscose solution is small and thereafter forming paper or a nonwoven fabric from the resulting dispersion.

The process according to the invention combines the process of rayon making with that of paper making. Using incompletely regenerated filaments with the primary swelling value of more than 1,900, which have been manufactured by spinning viscose having a high viscosity and a high 'y-value in a low acid concentration bath, a sheet of nonwoven fabric is formed on a sieving machine after the filaments have been cut and dispersed in Water.

3,553,078 Patented Jan. 5, 1971 Generally, the filaments have a residual -value of 15 or more and preferably of from 15 to 40.

The method used for determining the primary swelling value of incompletely regenerated cellulose filaments is as follows: The filaments (ca. 0.5 gram as dry cellulose) are steeped in distilled Water at 20 C. for 5 minutes. The swollen filaments thus obtained are centrifuged for 3 minutes by a force of 1,000 G and the weight (W) of the hydroextracted filaments is obtained. Thereafter the filaments are bone-dryed and the weight (W of the bonedry filaments is obtained. The primary swelling value is calculated from the following formula:

%=primary swelling value Such an improvement has in particular been attained by using a glass or porcelain spinneret developed recently, instead of a usual metal spinneret. The reason why a glass or a porcelain spinneret has such a merit can be explained as follows:

Certain kinds of liquids having a high viscosity, including a viscose solution, expand when extruded from a capillary. This phenomenon, e.g., the diameter of a spun filament is larger than that of the spinning orifice, is known as the Barns effect. Moreover, it has been found that the degree of expansion of a viscose solution corresponds inversely to the length-to-diameter ratio of a capillary.

In the case of a normal glass spinneret, the length-todiameter ratio of a hole is generally from 20 to 30, while the effective hole-length of a usual metal spinneret is generally only about twice the spinneret hole-diameter. This fact means that viscose filaments extruded from a normal glass spinneret expand less than those extruded from a usual metal spinneret, As the result, in the case of a glass spinneret, holes can be distributed more densely than in the case of a usual metal spinneret.

In wet spinning, a bundle of spun filaments retains a certain quantity of bath liquor in it during its travel in the bath after extrusion from a spinneret. The retained volume of bath liquor is proportional to the actual surface area of the spinneret, within Which the total number of holes is drilled. Therefore, the bundle extruded from a normal glass spinneret retains less bath liquor than that extruded from a usual metal spinneret, if both spinnerets have the same number of holes. If so, when spun in the same acid concentration bath, the quantity of bath liquor which is eifective per filament is considerably less in the case of a normal glass spinneret than in the case of a usual metal spinneret. This is the reason why incompletely regenerated filaments having a higher primary swelling value are obtainable through a normal glass spinneret and not through a usual spinneret, without any difiiculty and yet in a stable state by using a spinning bath having same acid concentration. From the fibres thus obtained a paper sheet is easily made on a sieving machine, which paper sheet looks like a textile fabric.

It is clear from the above that, although the improvement above-mentioned is attained by using a normal glass spinneret, the glass spinneret itself is not indispensable in the present process. The present invention can use any spinneret which makes the Barns effect of a viscose solution small. It is preferable in the process of the present invention to use a spinneret in which the effective lengthto-diameter ratio of holes is more than five.

The primary swelling value of incompletely regenerated filaments is apt to decrease after leaving the spinning bath, owing to the action of acid liquor still remaining on them. To prevent such lowering of the primary swelling value, it is preferred to wash oif the acid liquor on the filaments by passing them through a sodium sulphate solution at a temperature of less than 35 C. The concentration of sodium sulphate in the solution should be kept more than 50 g./l., otherwise the filaments may stick together and sulficient dispersion of the cut fibres will not be attained.

The following examples illustrate the invention.

EXAMPLE 1 Viscose with a DR of 460, a 'y-value of 60 and a viscosity giving rise to a falling-ball measurement of 270 seconds was spun using a glass spinneret having a lengthto-diameter ratio of 20 into a spinning bath containing 16 g./l. of sulphuric acid, 0.4 g./l. of zinc sulphate and 40 g./l. of sodium sulphate at a temperature of 16 C. with a bath residence time of 1.5 seconds, and incompletely EXAMPLE 2 Viscose with a DR of 650, a -value of 65 and a viscosity giving rise to a falling-ball measurement of 490 seconds was spun using a glass spinneret having a lengthto-diameter ratio of into a spinning bath containing 14 g./l. of sulphuric acid, 0.6 g./l. of zinc sulphate and 60 g./l. of sodium sulphate at a temperature of 30 C., and incompletely regenerated filaments, having a residual value of 24 and a primary swelling value of 3,100%, were obtained. The resulting filaments were cut without drying, dispersed immediately in water and shaped into a paper sheet. The wet sheet was bleached and dried after moderate pressing at a pressure of 20' kg./cm. The nonwoven fabric thus obtained had a drape of a plane fabric. The characteristics of the product are shown in the following table.

EXAMPLE 3 Viscose similar to that used in Example 2 was similarly spun into a spinning bath containing 13 g./l. of sulphruic acid, 0.7 g./l. of Zinc sulphate and 60 -g./l. of sodium sulphate at a temperature of 30 C., and incompletely regenerated filaments, having a residual y-value of 29 and a primary swelling value of 6,l90%, were obtained. The resulting filaments were out without drying, dispersed immediately in water and shaped into a paper sheet. The wet sheet was bleached and dried after moderate pressing at a pressure of 15 kg./ cm. The nonwoven fabric thus obtained had a drape of a cotton flannel. The characteristics of the product are shown in the following table.

EXAMPLE 4 Viscose similar to that used in Example 2 was similarly spun into a spinning bath containing 12 g./l. of sulphuric acid, 0.8 g./l. of zinc sulphate and 80 g./l. of sodium sulphate at a temperature of 30 C., and incompletely regenerated filaments, having a residual -value of 33 and a primary swelling value of 9,200, were obtained. The resulting filaments were cut without drying, dispersed immediately in water and shaped into a paper sheet. The Wet sheet was bleached and dried after moderate pressing at a pressure of 5 kg./cm. The nonwoven fabric thus obtained had a drape like that of towelling. The charac teristics of the product are shown in the following table.

4 EXAMPLE 5 Viscose similar to that used in Example 2 was spun into a low acid spinning bath containing 13.3 g./l. of sulphuric acid, 0.6 g./l. of zinc sulphate and 60 g./l. sodium sulphate at a temperature of 30C., and incom pletely regenerated filaments, having a residual 'y-Value of 26 and a primary swelling value of 3,300, were obtained. Similar filaments were treated with an aqueous solution containing g./l. of sodiumsulphate at a temperature of 15 0., immediately after leaving the spinning bath and the primary swelling value of the incompletely regenerated filaments thus obtained was 4,400, in comparison with 3,300 of those obtained without the said treatment.

*Breaking length given is the mean value of wire direction and cross direction Values.

What we claim is:

1. A process for manufacturing rayon paper or nonwoven fabric by a wet system, which comprises dispersing in water staple fibres formed from stable incompletely regenerated cellulose filaments obtained by the viscose process, said filaments having a primary swelling value of from 1,900 to 10,000 and being obtained by spinning viscose having a DR of more than 450 through a spinneret having an effective length to diameter ratio for the holes of the spinneret of more than five into a coagulating bath Which contains from 8 to 18 grams per litre of sulphuric acid, from 0.2 to 1.0 gram per litre of zinc sulphate and from 20 to 100 grams per litre of sodium sulphate at a temperature of from 15 to 35 C. and thereafter forming paper or a nonwoven fabric from the resulting dispersion.

2. A process according to claim 1, including the step of passing the spun filaments through an aqueous solution containing substantially 100 grams per'litre of sodium sulphate at a temperature of about 15 C., immediately after the filaments have left the coagulating bath.

3. A process according to claim 2, wherein the incompletely regenerated cellulose filaments are spun through a glass spinneret.

References Cited UNITED STATES PATENTS 3,156,605 11/1964 Anderer et al. 162l57(C) 3,320,117 5/1967 Aoki et al 162157(C) 3,341,645 9/1967 Horiuchi et al. 264188 FOREIGN PATENTS 6,806,435 5/1968 Netherlands 162-157(C) S. LEON BASHORE, Primary Examiner A. A. DANDREA, JR., Assistant Examiner US. Cl. X.R. 

